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03.15 GOLF COURSE MANAGEMENT 91
The three cool-season species — Kentucky
bluegrass, perennial ryegrass and tall fescue
— followed similar trends in carbon dioxide
fux across most measurement dates.
Carbon dioxide fux data within species
but across cultivars of varying growth rates
showed few differences.
Grass clipping management played a
minor role in greenhouse gas fux, as returning
grass clippings resulted in greater carbon diox
-
ide fux than collecting clippings on only one
of the six measurement dates. Nitrous oxide
fux was not different among main treatment
effects (species, cultivar and clipping manage
-
ment) during the experiment, and there was
not a measurable methane fux.
Differences in labile and total soil carbon
were realized between turfgrass species after
three years of growth post-planting, with tall
fescue having 9.9% more labile soil carbon
and 4.5% more total soil carbon than Ken
-
tucky bluegrass. After two years under differ-
ent mowing practices, plots where grass clip-
pings were returned had 3.3% more labile soil
carbon, 4.2% more total soil carbon and 4.6%
more total soil nitrogen than those where clip
-
pings were collected.
Planting slower-growing turfgrasses re
-
sulted in fewer annual mowing events: Ken-
tucky bluegrass required fewer annual mow-
ing events than tall fescue, and slow-growing
cultivars needed to be mowed less than the
moderate-growing cultivars, which were
mowed fewer times than the fast-growing cul
-
tivars (Table 1). Mowing by the one-third rule
also reduced mowing requirements (Table 1).
Returning clippings increased the num
-
ber of annual mowings by about 2 compared
to plots where clippings were collected when
mowed by the one-third rule (Table 1), but
returning grass clippings was benefcial as it
increased tissue nitrogen concentration in
clippings as well as total soil nitrogen concen
-
tration and total and labile soil carbon.
This project is one of many current proj
-
ects being conducted by turf scientists around
the country so that we can continue to learn
and better understand how turf management
infuences soil carbon sequestration. The re
-
sults of this study highlight the importance of
turfgrass selection and mowing practices on
the carbon and nitrogen dynamics and bio
-
geochemical cycling in a turfgrass system.
Aaron Patton (ajpatton@purdue.edu) is an associate pro-
fessor, Quincy Law is a graduate research assistant, and
Dan Weisenberger is a research agronomist in the depart
-
ment of horticulture and landscape architecture, and Jon
Trappe is a graduate research assistant and Ron Turco is
a professor in the department of agronomy at Purdue Uni
-
versity, West Lafayette, Ind.
Number of mowing events
Weekly One-third rule
Cultivar Species Growth rate
†
Collected Returned Collected Returned
Gazelle II tall fescue slow 28.25 29 16 17.75
Tar Heel II tall fescue medium 29 29.25 17.25 21.25
Endeavor tall fescue fast 28.75 29.5 21 24.25
Prosperity Kentucky bluegrass slow 19.75 24 12.25 14.25
Moonshine Kentucky bluegrass medium 27.5 28 15.5 17.5
Thermal blue Kentucky bluegrass fast 27.75 28 20 22.5
†
Cultivars were selected for this experiment based on their growth rate in preliminary trials and their similar appearance and stress tolerance in previous field trials in West
Lafayette, Ind. (data not shown).
Table 1. The number of recorded mowing events with clippings collected and returned for each treatment in 2013.
Recorded mowing events in 2013
Reducing annual bluegrass
in fairways
Zac Reicher, Ph.D.
Matt Sousek
David Minner, Ph.D.
Andrew Hoiberg, Ph.D.
Annual bluegrass (Poa annua) is the most
(Report)
troublesome weed on golf courses wherever
cool-season grasses are grown. On fairways in
particular, populations can quickly approach
50% or more if aggressive control measures
are not initiated shortly after establishment.
Furthermore, diffcult summers can cause sig
-
nifcant thinning or widespread death of an-
nual bluegrass.
In response, superintendents will overseed
in late August to early September to help the
stand recover from summer. However, an
-
nual bluegrass germination and competition is
highest in the fall, and thus it can overtake the
desired turf and the cycle starts over. Mini
-
mizing annual bluegrass and maximizing the
desired cool-season turf could help break this
cycle. Seeding early in the summer before the
almost inevitable annual bluegrass thinning
could allow the desired turf to establish while
the annual bluegrass is thinning. Addition
-